A hinge apparatus makes two members spaced from each other or folded one member over another around a shaft, according to necessity. A representative example of the hinge apparatus is a left/right rotational hinge apparatus including a horizontal actuator which is used between a door and door frame, or an up/down rotational hinge apparatus including a vertical actuator which is used for a refrigerator, a mobile phone, or a notebook computer.
A conventional hinge apparatus having an automatic return function is disclosed in Korean Laid-open Patent Publication No. 2001-0027832.
In the case of the conventional hinge apparatus, a conversion head which ascends and descends according to rotation of a door is guided by a pair of guide pins, and the guide pins are fixed to four hinge knuckles. Also, a cylinder and the conversion head are incorporated in the four knuckles. Accordingly, when the movable hinge knuckles receive big load and rotate for a long time, durability of the hinge apparatus is lowered and the structure is complicated. As a result, an assembly productivity deteriorates.
Also, since a compression spring for performing an automatic return function of a door cannot provide a large restoring force at the time of automatic return of a door, it is difficult to apply the conventional hinge apparatus in a large-size door. Also, since a fixing unit for temporarily fixing the door is not installed in the conventional hinge apparatus, the door does not rotate at the state where the door has been opened at a predetermined angle. Accordingly, it is inconvenient for users to use the conventional hinge apparatus.
Meanwhile, Korean Utility Model Registration No. 0271646 discloses a hinge type door opening and closing apparatus in which a hydraulic type door closer and a spring type door closer are separately configured and the former and the latter are combined with each other.
Meanwhile, the conventional art has not proposed an optimized structure of a left/right rotational door hinge apparatus which is applied in a large-size door.
Also, Korean Utility Model Registration No. 435188 discloses a hinge apparatus using a single camshaft having a spiral cam diagram whose multi-stage automatic return speed establishment structure is stabilized. However, a restoring force required at the time of closing a door cannot be obtained from the hinge apparatus. As a result, the door closing force is reduced and accordingly an automatic return of the door is not smoothly accomplished.
Further, in the case of a hinge apparatus having an automatic return function for a large-size door employing a double camshaft which has been proposed by the same applicant as the present invention in Korean Laid-open Patent Publication No. 2006-18461 on Mar. 2, 2006 (corresponding to Korean Patent Application No. 2004-66832 on Aug. 24, 2004), an upper camshaft which is installed in order to compensate for reduction of a door closing force includes a pair of spiral ascending/descending holes, like a lower camshaft. The spiral ascending/descending holes may cause the rotational force to vary in the vertical direction when a piston rod and a valve are operated by the rotating camshaft, to accordingly cause a loss of 30% or so. As a result, the upper camshaft does not play a big role of improving the door closing force, and has a problem that the overall length of the upper camshaft is somewhat long.